1. Field of the Invention
The present subject matter relates generally to manufacturing a Light Emitting Diode (LED) micro-display on an Active Matrix (AM) panel, and more specifically to manufacturing an LED micro-display on an AM panel using flip-chip technology.
2. Related Art
LED array displays made with individually packaged devices have been widely used for various applications. In recent years, different techniques have been exploited to fabricate monolithic, passively-addressable LED arrays. The array dimensions and pixel brightness in conventional passively-addressable LED arrays were limited by the loading effect in the same row or column. Thus, various new address schemes and fabrication technologies are suggested to improve the operating effectiveness of monolithic LED arrays.
For example, U.S. Pat. Nos. 5,789,766, 5,827,753, and 5,893,721 relate to methods of fabricating an LED array and driving circuitry that includes sequentially forming overlying layers of material on the surface of a semiconductor substrate, the layers cooperating to emit light when activated. The insulating layer is formed on the layers and the layers are isolated into an array area and the driver circuitry area with row and column drivers dividing the array area into an array of LEDs arranged in rows and columns. Row and column driver circuits are formed on the insulating layer in the driver circuitry area. Row buses individually couple each LED in the array to corresponding driver circuits. But the circuitry layer formed on the insulating layer can only be a thin film device like a-Si TFT or poly-Si TFT, however, these have low field effect mobility and cannot provide enough current for the LEDs. On the other hand, these three patents adopt a bottom-emitting configuration and the aperture of the array is limited by the circuitry area, thereby resulting in a relatively low light efficiency.
U.S. Patent Application Publication No. 2008/0194054 relates to a method of fabricating an LED array package structure having a silicon substrate. The LED array package structure includes a silicon substrate having a plurality of cup-structures thereon, a reflective layer disposed on the silicon substrate, a transparent insulation layer disposed on the reflective layer, a conductive layer disposed on the transparent insulation layer and a plurality of LEDs disposed respectively on the conductive layer in each cup-structure. In this way, the LED array can only operate in a passive mode and each LED size is as large as tens millimeters. Hence, the LEDs made by this method often suffer from bad illumination uniformity and the low resolution.
U.S. Pat. No. 6,975,293 relates to five types of driving circuits for an active matrix LED display. The circuits are composed of four MOS transistors, each of which has a drain and a source. An anode of an LED is coupled to a source of a driving transistor and a cathode of the LED is coupled to a second voltage. These methods are suitable for an OLED array display, but not suitable for an LED micro-display array because the LED process is not compatible with the CMOS process.
U.S. Patent Application Publication No. 2008/0171141 relates to methods of fabricating LED array structures including multiple vertical LED stacks coupled to a single metal substrate. Such an LED array may offer better heat conduction and an improved matching of LED characteristics (e.g., forward voltage and emission wave length) between the individual LED stacks compared to conventional LED arrays. But the LED array in this reference can only act as a single LED which can only light on and off together and cannot control the LED pixel individually and precisely.